BlazeGraph/wikibase:label performance - Wikidata

25 Nov 2018

Hi,

I just noticed that BlazeGraph takes an undue amount of time for a 
rather simple type of queries. The following times out:

SELECT ?item ?itemLabel
WHERE
{
   ?item wdt:P31 []
   SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }
} LIMIT 10

Manually forcing a specific query plan makes the query work in <200ms:

SELECT ?item ?itemLabel
WHERE
{
   { SELECT * WHERE { ?item wdt:P31 [] } LIMIT 10 }
   SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }
}

But of course the original query should normally be streaming and not 
depend on any such smartness to push LIMIT inwards.

Cheers,

Markus